Articles of footwear can include an upper, a midsole, and an outsole. The upper can include layers or sections of material that wrap about a substantial portion of the superior, anterior, posterior, medial and lateral portions of the wearer's foot. The upper can also include laces, straps, or the like for securing the footwear to the wearer's foot. The outsole can be a unitary piece of relatively high-friction material that provides traction for the footwear. Also, the midsole can include foam that is disposed between the outsole and the upper for providing cushioned support for the wearer.
In some cases, footwear can additionally include a bladder that contains a fluid, such as a gas or gel. The bladder can be embedded within the midsole, and weight of the wearer and other loading on the bladder can cause the fluid to displace within the bladder. As such, the bladder can resiliently deform and conform to the wearer's foot in order to provide better support and comfort than some midsoles made entirely out of foam. Also, the bladder can dampen or attenuate shock loads or other loads during jumping, running, and other activities to provide better cushioning.
Although conventional footwear with bladders have been adequate for their intended purposes, they do suffer from certain disadvantages. For instance, manufacturing of the footwear can be significantly expensive and complicated. For instance, the bladder itself increases the part count of the footwear. Also, the bladder is typically manufactured separately from the rest of the sole assembly, and then the bladder is assembled into the sole assembly. As such, the bladder can increase part costs and manufacturing costs.
Furthermore, sole assemblies that include fluid-filled bladders can significantly increase the weight of the sole structure, which can hinder the wearer's running, jumping, or other movements. Even further, such sole assemblies can be difficult to recycle because the assembly includes multiple parts as discussed above.